An augmented reality (AR) device allows virtual display to combine and interact with real world scenes in a user's view. The AR device must use appropriate optical structures to produce optical see-through (OST) images. Conventional AR devices can be separated into two types: projector-style and waveguide-style.
A projector-style AR device uses a micro projector and a micro display to project the virtual image, and a partially-reflecting optical combiner to reflect and magnify the virtual image into the user's eye while letting the real world scenes through, combining the virtual image and the real world scenes to provide AR effect.
The optical combiner is usually a freeform optical component having optical power, and hence an extra freeform corrector is needed to correct for distortion of the real world scenes. Furthermore, the field of view (FOV) of the projector-style AR device is directly related to the size thereof. According to geometric optics, let the eye-relief of the projector-style AR device be D and FOV be α, the diameter of the optical combiner must be larger than or equal to 2D tan(α/2). Thus, if the size of the projector-style AR device is to be kept compact, then the FOV thereof would not be large enough to allow for an immersive experience.
In a waveguide-style AR device, an optical component directs light emitted from a micro display into a waveguide, and the light is outputted into the user's eye from the waveguide using another optical component after transmitting a certain distance in the waveguide. Since the waveguide is light-transmissible, ambient light of the real world scenes can pass through the waveguide at the same time. The aforementioned optical components may be a geometric optical mirror, a diffractive optical element (DOE), or a holographic optical element (HOE).
However, the FOV of the waveguide-style AR device is also limited by the properties of the aforementioned optical components and by the condition for total internal reflection in the waveguide. Due to a number of restrictions, the diagonal FOV of the waveguide-style AR device is usually no larger than 50°.